Showing papers by "University of Melbourne published in 1982"

On the mechanism of wall turbulence

Abstract: In this paper an attempt is made to formulate a model for the mechanism of wall turbulence that links recent flow-visualization observations with the various quantitative measurements and scaling laws established from anemometry studies. Various mechanisms are proposed, all of which use the concept of the horse-shoe, hairpin or ‘A’ vortex. It is shown that these models give a connection between the mean-velocity distribution, the broad-band turbulence-intensity distributions and the turbulence spectra. Temperature distributions above a heated surface are also considered. Although this aspect of the work is not yet complete, the analysis for this shows promise.

The acquisition of phosphorus byLupinus albus L.

Abstract: It has been demonstrated by an agar film technique thatL. albus can cause the breakdown of colloids of iron/silicate, iron/phosphate, aluminium/silicate and aluminium phosphate and destabilise suspensions of manganese dioxide, calcium mono-hydrogen phosphate and ferric hydroxide. Dissolution of these compounds was most marked in areas adjacent to proteoid roots (dense clusters of secondary laterals of limited growth which develop on lateral roots) and parts of the tap root. Soil associated with these regions of the root system contained more reductants and chelating agents than the bulk soil. Soil from around the roots ofL. albus exhibited much greater reducing and chelating activity than that associated with the roots of rape and buckwheat.

The Mean Shape of the Human Cornea

Abstract: The anterior surface of the cornea is the major refracting element in the human eye. Knowledge of its shape and the variation of this shape throughout the population are important in calculations of the corneal contribution to ocular aberrations. Since the cornea is the surface on which the contact lens rests, the corneal shape is also of importance in contact lens design. this paper presents results of the fitting of a conicoid equation to corneal shape data derived from a precision photokeratoscope. Both rotationally symmetric and non rotationally symmetric form of the conicoid equation were developed. The results show that if the cornea is regarded as a rotationally symmetric conicoid, the conicoid is ellipsoidal but with insufficient asphericity to eliminate spherical aberration for distance vision. More importantly, the results show that the cornea is significantly asymmetric in both radius of curvature and asphericity

The vortex-shedding process behind two-dimensional bluff bodies

Abstract: Using a variety of flow-visualization techniques, the flow behind a circular cylinder has been studied. The results obtained have provided a new insight into the vortex-shedding process. Using time-exposure photography of the motion of aluminium particles, a sequence of instantaneous streamline patterns of the flow behind a cylinder has been obtained. These streamline patterns show that during the starting flow the cavity behind the cylinder is closed. However, once the vortex-shedding process begins, this so-called ‘closed’ cavity becomes open, and instantaneous ‘alleyways’ of fluid are formed which penetrate the cavity. In addition, dye experiments also show how layers of dye and hence vorticity are convected into the cavity behind the cylinder, and how they are eventually squeezed out.

The mean shape of the human cornea

Abstract: The anterior surface of the cornea is the major refracting element in the human eye. Knowledge of its shape and the variation of this shape throughout the population are important in calculations of the corneal contribution to ocular aberrations. Since the cornea is the surface on which the contact lens rests, the corneal shape is also of importance in contact lens design. this paper presents results of the fitting of a conicoid equation to corneal shape data derived from a precision photokeratoscope. Both rotationally symmetric and non rotationally symmetric form of the conicoid equation were developed. The results show that if the cornea is regarded as a rotationally symmetric conicoid, the conicoid is ellipsoidal but with insufficient asphericity to eliminate spherical aberration for distance vision. More importantly, the results show that the cornea is significantly asymmetric in both radius of curvature and asphericity

Overgrowth in a marine epifaumal community: Competitive hierarchies and competitive networks.

Abstract: The frequencies with which organisms of a species overgrew or were overgrown by organisms of other species in a marine epifaunal community were estimated. The ranking of the ability of the major taxonomic groups to overgrow others was basically hierarchical:ascidians≧sponges>bryozoans>barnacles, polychaetes, tubicolous amphipods, hydroids. In contrast, the ranking of the competitive ability of species in the community did not form a simple linear hierarchy and there was no single competitively dominant species (measured in terms of overgrowth). There were often no significant differences in the ability of species to overgrow each other within the three major taxonomic groups of sponges, ascidians and bryozoans. Such results were common also between the species of large sponges and ascidiams which dominated substrata immersed for periods longer than two years. A lack of a significant difference in the competitive ability of species was usually the result of (a) frequent formation of delay/ties or “standoffs” and (b) changes in the outcome of interactions due to change in the relative size of interacting colonies. In many two-species interactions the species which had the larger colony in a given encounter had a greater probability of winning. When the range of colony sizes of two species was similar there was often no significant difference between the competitive ability of each species. Such cases without a clearcut winner often represented a backloop in an otherwise hierarchical sequence of competitive ability, i.e. Species A beats Species B, Species B beats Species C, no significant differences in competitive ability between Species C and A. No examples of competitive networks of the form Species A beats Species B, Species B beats Species C, Species C beats Species A were found. Backloops in otherwise hierarchical sequences (no significant differences in competitive ability) occurred most frequently between species within the same major taxonomic groups and were the result of a very even balance in the generalised competitive mechanism of overgrowth. It seems probable that backloops in hierarchical sequences are more commonly due to the absence of clear competitive dominance in interactions between species (reversals in the outcome of overgrowth interactions and “standoffs”), rather than to direct backloops formed by a specialised or to a generalised competitive mechanism. Network-like arrangements of competitive ability formed by the type of processes described here are likely to contribute significantly to the high levels of species diversity observed in many marine epifaunal communities subject to low levels of physical disturbance.

Hydatidosis/cysticercosis: immune mechanisms and immunization against infection.

Abstract: Publisher Summary The hydatidosis/cysticercosis disease complex is caused by infection with the larval stages of tapeworms belonging to the family Taeniidae. It is a threat to the people because of its effect on human health and on the food-animal industries. This chapter focuses on the larval cestodes of the family Taeniidae. There have been significant recent advances in the immunological diagnosis of the cysticercoses and, especially in hydatid disease of man. Factors determining the innate resistance to infection with larval taeniid cestodes not only play an important part in determining the epidemiology of natural infection with larval cestodes but also have a central role in the critical evaluation and interpretation of research data concerning immunity to these parasites. The intermediate hosts of all larval taeniid cestodes, thus, far examined manifest an impressive level of acquired immunity to reinfection. The propagation of taeniid cestodes depends on the evolution and persistence of predator–prey relationships between definitive and intermediate hosts and on the survival of tissue-invading larval stages for the remaining life of infected individuals. When pathological complications override the benign tolerance on the part of the host, they often involve acute inflammatory episodes, specifically triggered by the release or exposure of antigens that have previously sensitized the individual. Cysticercosis and hydatidosis are, especially prevalent amongst the rural poor of the world and attention to them is demanded as a critical component of the development process.

Molecules stimulating early red cell, granulocyte, macrophage, and megakaryocyte precursors in culture: similarity in size, hydrophobicity, and charge.

Abstract: Molecules in conditioned medium from stimulated lymphocyte populations or from certain cell lines are known to stimulate cells committed to various hemopoietic lineages as well as pluripotential cells to form colonies in culture. In this study, the relationship between molecules active on pluripotential cells and early cells committed to granulocyte, macrophage, megakaryocyte, or red cell production was explored using techniques of chemical separation. After separation on the basis of charge, or after sequential purification using methods of high resolving power based on hydrophobicity and size, these activities remained associated with one another. The observations provide support for a model which proposes that pluripotential hemopoietic precursor cells as well as their early committed progeny may all be responsive to a single lineage-indifferent factor. Responsiveness to "lineage-specific" factors such as erythropoietin is proposed to be a feature only of later cells after they have made the appropriate receptors as part of their differentiation program.

The effect of genetic background on the fitness of diazinon resistance genotypes of the Australian sheep blowfly, Lucilia cuprina

Abstract: Laboratory and field experimentation has shown that resistant and susceptible diazinon genotypes of flies collected from the field may have similar fitness in an environment free of diazinon. If the genetic background of resistant genotypes from the field is disrupted, the fitness of the resistant genotype declines. These results, in conjunction with previous data, indicate a modification of the genetic background in field populations following the spread of the resistance allele some ten years earlier. It is suggested that this outcome is dependent on the availability of genetic variability, the intensity of selection and the duration of insecticide usage after resistance develops.

Two-factor requirement for murine megakaryocyte colony formation.

Abstract: WEHI-3 cell-conditioned medium with the capacity to stimulate megakaryocyte colony formation was separated by Sephadex G-150 column chromatography. The development of colonies containing megakaryocytes was observed only when mixing experiments were performed. Individual fractions did not support megakaryocyte colony growth. The two factors in WEHI-3 CM required for megakaryocyte colony growth had apparent average molecular weights of 35,000 daltons (megakaryocyte CSF) and 100,000 daltons (megakaryocyte potentiator). The results were confirmed in serum-free conditions in which colonies were directly identified in the cultures by acetylcholinesterase staining. Two growth factors may be necessary for the genesis of megakaryocytic colonies.

Detection of a Rotavirus-Like Agent Associated with Diarrhea in an Infant

Abstract: A rotavirus-like agent was detected in the feces of a child with diarrhea. Although morphologically indistinguishable from rotavirus, the agent was serologically distinct, and electrophoresis of its nucleic acid also showed that it was dissimilar. Images

Ultrastructural and tissue-culture studies on the role of fibronectin, collagen and glycosaminoglycans in the migration of neural crest cells in the fowl embryo

Abstract: The initial migration of neural crest (NC) cells into cell-free space was studied by transmission electron microscopy at trunk levels of fowl embryos, some of which were fixed in the presence of ruthenium red. Migrating NC cells occurred in zones which contained fewer ruthenium-red stained 15–40 nm diameter granules than other regions. The ruthenium-red stained granules were linked by similarly stained thin (⪖ 3 nm diameter) microfibrils. The granules resemble proteoglycan and the microfibrils may be hyaluronate. NC cells contacted thicker (⪖ 10 nm diameter) fibrils and interstitial bodies, which did not require ruthenium red for visualization. Cytoplasmic microfilaments were sometimes aligned at the point of contact with the extracellular fibrils, which may be fibronectin and collagen. Phase-contrast time-lapse videotaping and scanning electron microscopy showed that NC cells of the fowl embryo in vitro migrated earlier and more extensively on glass coated with fibronectin-rich fibrous material and adsorbed fibronectin molecules than on glass coated with collagen type I (fibres and adsorbed molecules). NC cells became completely enmeshed in fibronectin-rich fibres, but generally remained on the surface of collagen-fibre gels. When given a choice, NC cells strongly preferred fibronectin coatings to plain glass, and plain glass to dried collagen gels. NC cells showed a slight preference for plain glass over glass to which collagen was adsorbed. Addition to the culture medium of hyaluronate (initial conc. 20 mg/ml), chondroitin (5 mg/ml) and fully sulphated chondroitin sulphate and dermatan sulphate (up to 10 mg/ml) did not drastically alter NC cell migration on fibronectin-rich fibrous substrates. However, partially desulphated chondroitin sulphate (5mg/ml) strongly retarded the migration of NC cells. The in vivo and in vitro studies suggest that fibronectin may dictate the pathways of NC cell migration by acting as a highly preferred physical substrate. However, the utilization of these pathways may be reduced by the presence of proteoglycans bearing undersulphated chondroitin sulphate.

A model accounting for effects of vibratory amplitude on responses of cutaneous mechanoreceptors in macaque monkey

Abstract: 1. A mechanoreceptor model, developed in the preceding paper (Freeman & Johnson, 1982), was used to study the effects of vibratory intensity and frequency on the responses of slowly adapting, rapidly adapting and Pacinian afferents in monkey hairless skin. As in the previous paper almost all of the response properties studied here were accounted for by the equivalent circuit model; changes in membrane time constant and amplitude sensitivity accounted for the differences between the three mechanoreceptive fibre types.2. The stimulus-response function of primary concern was the relationship between impulse rate and vibratory amplitude. This relationship had the same general form in each of the three fibre types. Amplitudes, I, less than I(0) produced no impulse on any stimulus cycles. Amplitudes greater than I(1) produced one impulse on every cycle. As I rose from I(0) to I(1) the impulse rate rose monotonically from 0 to 1 impulse/cycle. For each fibre type the form of this ramp depended on the stimulus frequency.3. At stimulus frequencies low in the frequency range of each fibre type the (I(0), I(1)) ramp tended to be steep and sigmoidal in shape. Two or more impulses occurred on some cycles and none on others.4. At intermediate frequencies the (I(0), I(1)) ramps became linear with at most one impulse on each cycle. A short plateau appeared at 0.5 impulses/cycle (i.e. there was a range of intensities yielding one impulse on alternate cycles). All of these response properties at low and intermediate frequencies were explained by the model.5. At higher frequencies the (I(0), I(1)) ramps became shallower and developed discontinuities in slope at impulse rates of 0.5 impulses/cycle. At stimulus frequencies greater than 20 Hz for SAs and RAs, the upper segment of the (I(0), I(1)) slope became steeper. For frequencies greater than 80 Hz, the upper segments of the Pacinian (I(0), I(1)) slopes were shallower than the lower segments. These effects suggested transient periods of hyperexcitability following each action potential, and reductions in sensitivity due to high impulse rates, respectively.6. The model's membrane time constant was adjusted to match the observed reduction in the (I(0), I(1)) slope with increasing stimulus frequency. The time constants required for least-squares fitting were 58, 29 and 4.2 msec for slowly adapting, rapidly adapting and Pacinian afferents, respectively; these values are of the same order as those obtained in the preceding paper.7. Receptor sensitivity varied across the frequency spectrum, slow adaptors being most sensitive at low frequencies, rapidly adapting units at mid-range, and Pacinians at the high frequencies. According to the model, the high frequency roll-off in a receptor's tuning curve is due to the current integrating properties of receptor membrane, and the low frequency roll-off is due to a high pass filter, presumably mechanical, situated in the tissues between the stimulus probe and receptor membrane.8. Impulse phase advances with increasing stimulus intensity in both receptor and model. The ability of the model to fit both the rate-intensity function and phase advance functions in individual receptors is demonstrated.

Age at menarche, urine estrogens and breast cancer risk.

Abstract: In 511 nulliparous women aged 15-19 years and 347 aged 30-39, an analysis has been undertaken of the relationship of urine concentrations of the three principal estrogens to age, age at menarche and Quetelet's index of adiposity. The analysis was undertaken by means of multiple regression, controlling for each of the 12 centers from which the data originated, as well as for the other study variables. In the younger women, age was strongly and positively related to concentrations of E1 and E2 and less so to E3. In the age group 30-39, follicular phase specimens showed positive relationships with age for all three fractions but luteal specimens did not. Age at menarche showed inverse relationships to levels of E1 and E2 which were significant in the younger but not in the older age group. The associations of estrogens with Quetelet's index were weak and not statistically significant. The data suggest that women whose menarche occurs early not only have a longer duration of exposure to estrogens during years which are probably important in the initiation of breast cancer but, in addition, their exposures are at a higher level during those years and probably at later ages also. These observations support the hypothesis that the mechanism of the association of early menarche with breast cancer risk is via the association of both with estrogen stimulus.

Cutaneous mechanoreceptors in macaque monkey: temporal discharge patterns evoked by vibration, and a receptor model

Abstract: 1. Vibratory stimuli applied to the hand of a monkey evoke phase locked impulse trains in the three classes of low threshold mechanoreceptive afferents which innervate the area. The responses of each class of afferent (slowly adapting (SA), rapidly adapting (RA), and Pacinian (PC) vary in a systematic but complex way across the range of frequencies and intensities to which they are sensitive. The receptors are not accessible for electrophysiological recording. The aim in this study was to infer the mechanisms underlying their responses from detailed examination of the statistical properties of the impulse trains. 2. A very simple receptor model with four degrees of freedom was chosen as a starting point. The independent variables consisted of the resting membrane time constant, τ, a variable membrane conductance, Gr, the fraction of each sinusoidal stimulus cycle producing depolarization, pr, and the noise level, σ, which was assigned to the impulse threshold. The aim was to use the deviations between observed data and predictions from the basic model to construct a more effective model. In fact, the deviations were minor and were mostly explained by periods of increased excitability in the wake of each action potential. Almost all of the differences between the responses of the three mechanoreceptive classes examined in this paper were accounted for by differences in time constants. 3. The temporal structure of the responses from each mechanoreceptive class was examined at two levels of resolution, a coarse level where the resolution unit was a full cycle, and a fine level where the unit was 0·1 ms. 4. The coarse structure of each response was represented by the presence or absence of an impulse on each stimulus cycle. In each mechanoreceptive class, the impulse sequences were random at low stimulus frequencies and regular at high frequencies. The transition frequencies were roughly 5 Hz for the slowly adapting afferents, 7 Hz for the rapidly adapting afferents, and 110 Hz for the Pacinian afferents. The model matched these data closely when the time constants were set at 80, 60 and 3·4 ms for SAs, RAs and PCs, respectively. 5. The fine structure of the responses of each mechanoreceptive class exhibited impulse phase locking, phase advance with increasing intensity, and bimodal phase distributions at higher frequencies. Impulses contributing to the first mode of bimodal distributions always occurred in cycles following cycles in which no impulse occurred. Impulses contributing to the retarded mode always occurred in cycles following filled cycles. The mean phase differences between the two modes was called phase retardation. Phase retardation grew with stimulus frequency for both the receptors and the model; the time constants required to match the model against neural phase retardation curves were 123, 64 and 4·8 ms for SAs, RAs and PCs, respectively.

Effects of cimetidine and ranitidine on hepatic drug metabolism

Abstract: Cimetidine has been shown to impair elimination of a number of drugs metabolized by the hepatic mixed-function oxidase enzymes. It is uncertain whether this is related to its histamine H2-receptor antagonism or to its intrinsic structure. Ranitidine is a more potent H2-receptor antagonist and has a completely different structure. Cimetidine (1 gm/day for 7 days) induced a 23% and 35% fall in mean systemic clearance of antipyrine and theophylline, whereas ranitidine (300 mg/day 7 days) had no significant effect on the clearance of either drug. Our data suggest that the inhibition of drug metabolism by cimetidine is not related to histamine H2-receptor antagonism.

Age at menarche, probability of ovulation and breast cancer risk.

Abstract: An analysis is undertaken of the frequency of ovulation in 17 groups of women aged 15 to 19 who had been the subjects of other studies. A urine specimen of at least 8 h accumulation had been provided on the 20th or 21st day of a menstrual cycle by 681 women. Analysis is restricted to 431 specimens which had been collected between 11 and 3 days prior to the onset of the subsequent menstrual period. A pregnanediol concentration of less than 1 mg per litre in such a specimen was taken as evidence that the cycle was anovular. The probability of a cycle being anovular was inversely and significantly related to the number of years since menarche, and, with years since menarche held constant, was positively but not significiantly associated with age at menarche. This observation indicates that women with early menarche do not have a longer duration of exposure to anovular cycles than do those whose menarche is delayed, and that variation in the duration of exposure to post-menarcheal anovular cycles does not explain the association of breast cancer risk with early age at menarche. The 17 groups of women were classified into four categories according to ethnic origin and breast cancer incidence in the populations from which they derived. Anovular cycles were not more common in the high-risk groups; indeed, the two centers in the lowest risk category had the highest proportion of anovular cycles.

Numerical studies of surface-tension effects in nonlinear Kelvin-Helmholtz and Rayleigh-Taylor instability

Abstract: We consider the behaviour of an interface between two immiscible inviscid incompressible fluids of different density moving under the action of gravity, inertial and interfacial tension forces. A vortex-sheet model of the exact nonlinear two-dimensional motion of this interface is formulated which includes expressions for an appropriate set of integral invariants. A numerical method for solving the vortex-sheet initial-value equations is developed, and is used to study the nonlinear growth of finite-amplitude normal modes for both Kelvin-Helmholtz and Rayleigh-Taylor instability. In the absence of an interfacial or surface-tension term in the integral-differential equation that describes the evolution of the circulation distribution on the vortex sheet, it is found that chaotic motion of, or the appearance of curvature singularities in, the discretized interface profiles prevent the simulations from proceeding to the late-time highly nonlinear phase of the motion. This unphysical behaviour is interpreted as a numerical manifestation of possible ill-posedness in the initial-value equations equivalent to the infinite growth rate of infinitesimal-wavelength disturbances in the linearized stability theory. The inclusion of an interfacial tension term in the circulation equation (which stabilizes linearized short-wavelength perturbations) was found to smooth profile irregularities but only for finite times. While coherent interfacial motion could then be followed well into the nonlinear regime for both the Kelvin-Helmholtz and Rayleigh-Taylor modes, locally irregular behaviour eventually reappeared and resisted subsequent attempts at numerical smoothing or suppression. Although several numerical and/or physical mechanisms are discussed that might produce irregular behaviour of the discretized interface in the presence of an interfacial-tension term, the basic cause of this instability remains unknown. The final description of the nonlinear interface motion thus awaits further research.